We are fused (kiln- fired) glass artists and have a strong background in ceramic kilns as well...we would
NEVER use
any glazed or unfinished tile in the oven for the reasons stated above. Lots of poison out there. Should have stated these concerns more clearly in my earlier post...and it's why I'm so PO'd at these manufacturers for not addressing this issue...they are well aware that users are trying a variety of home-made "remedies" in order to work a way around the fact that many ovens are, for the most part, cheaply made, inferior designs.